One type of drum washing machine comprises an outer cabinet, a water tub mounted in the cabinet, and a plurality of elastic support mechanisms. Each support mechanism comprises a coil spring provided on an upper portion of the wash tub for elastically suspending the water tub and an anti-vibration damper provided on a lower portion of the water tub for damping vibration of the water tub. A friction damper is generally used as the anti-vibration damper. The friction damper utilizes a frictional resistance produced by a piston slid in a cylinder. Thus, the above-mentioned drum washing machine necessitates spaces over and below the water tub in which the coil springs and the anti-vibration dampers are disposed respectively.
Another type of drum washing machine comprises a plurality of elastic support mechanisms each of which includes an anti-vibration damper in which the piston and coil spring are disposed in the cylinder. This type of drum washing machine can achieve a reduction in the size thereof since it requires no spaces in which the coil springs are disposed.
The foregoing friction damper includes the piston and a sliding face of the cylinder each of which requires a high level of precision. The frictional resistance between the piston and cylinder is susceptible of aged deterioration due to influences of wear or the like. Accordingly, the friction damper has a low reliability concerning a long time of service.
To overcome the foregoing problem, the applicant of the present application filed a patent application in Japan for the invention providing a drum washing machine including an elastic support mechanism in which a predetermined amount of damping oil is contained in a cylinder of an anti-vibration damper. The patent application was published under publication No. 2001-212395. Referring to FIG. 13, the elastic support mechanism 1 comprises an anti-vibration damper 5 including a double cylinder 2, a predetermined amount of damping oil 3 contained in the cylinder and a piston 4 disposed in the cylinder and having an orifice 4a. The mechanism further comprises a coil spring 6 which is disposed in a lower interior of the cylinder 2 so as to be located below the piston 4 as shown in FIG. 13. A piston rod 9 extends upward from the piston 4 through a central hole of a cap closing an upper opening of the cylinder 2. The piston rod 9 has an upper end held by a nut 12 on a tub mount 7 provided on a water tub (not shown) with a cushioning member 11 interposed therebetween. A rod 10 mounted on a lower end of the cylinder 2 is held by another nut 12 on a bottom plate 8 of the outer cabinet with another cushioning member 11 interposed therebetween.
In the above-described anti-vibration damper 5, a damping effect can be achieved by viscous resistance of the oil 3 passing through orifices 4a with vertical movement of the piston 4. Accordingly, the frictional resistance between the piston 4 and cylinder 2 is less susceptible of aged deterioration such that the service life of the damper can be improved.
However, the foregoing support mechanism 1 has the following deficiencies. The cap 13 is welded to the upper end of the cylinder 2 so that the cylinder is hermetically sealed. FIG. 13 shows a welded portion Y. The coil spring 6 needs to be maintained in a compressed state when the cap 13 is welded to the cylinder 2. This reduces an assembling efficiency.
Furthermore, specifications of the coil spring 6 including spring constant, wire diameter, outer diameter, number of turns, length in the natural state, etc. are set on the basis of load (initial load, maximum load) applied to the elastic support mechanism 1, location of the water tub in the outer cabinet, and the like. Since the coil spring 6 is disposed in the cylinder 2, the outer diameter and length of the coil spring 6 in the natural state need to be matched with an inner diameter and length of the cylinder 2. As a result, the degree of freedom in the design of the elastic support mechanism 1 is reduced.
Additionally, if the coil spring 6 disposed in the cylinder 2 should fail, the whole mechanism 1 would need to be replaced by a new one. This reduces the recycling efficiency.